Complement factor I Complement factor I complex formation Authored: Jupe, S, 2010-10-26 Complement factor I (CFI) is a complex of one heavy and one light chain, both cleaved from the same precursor peptide. It inactivates complement subcomponents C3b, iC3b and C4b by proteolytic cleavage of the alpha chains of C4b and C3b in the presence of cofactors such as Factor H, C4b binding protein, Complement receptor 1 (CR1) or MCP (CD46). Edited: Jupe, S, 2010-11-01 Pubmed2956252 Pubmed301546 Reactome Database ID Release 43976801 Reactome, http://www.reactome.org ReactomeREACT_118674 Reviewed: Bradley, DT, 2012-02-13 Reviewed: Fraczek, LA, 2012-02-13